Pollinating Berry Crops

For some berry crops it has been shown that removal of all insect pollination leads to a 40% drop in fruit production. In addition the quality of non-insect pollinated fruit is significantly lower [3]. To obtain a large, well-formed berry most of the individual pistils in the flower should be pollinated. Inadequate pollination results in smaller or imperfect fruit since not all seeds and drupelets are formed. To obtain good pollination each flower needs to be visited 5 or more times preferably over 4 or more days[4].

For optimal pollination, bees must be collecting and distributing the pollen.

When bees visit flowers they are after either nectar or pollen. They will always collect a bit of both, however they tend to focus on either pollen or nectar. Pollen foragers are around 10 X more effective at pollination. In general, for blueberries this is not a problem as the hives are in a growth phase and require large amounts of pollen. For raspberries this can be a problem as hives are usually stronger and focus more on the heavy nectar flow provided. In the later parts of the blooming season, hives may start filling all available space resulting in a significant slowdown in brood production. This will lead to a reduction in pollen foraging first and then nectar foraging. Therefore it is very important that beekeepers are managing the hive and ensuring that it is functioning optimally. This generally means that the beekeeper should be examining the hives every 2-3 weeks.

The effectiveness of bees in pollinating plants

There are several different species of bees that are used commercially for pollination: honeybees, bumblebees, orchard mason bees and leaf cutter bees. All of these bees have their uses for specific crops. In general, bumblebees are the most effective pollinators; They gather more pollen because they are hairier and larger and have developed the ability to buzz or shake in the flower and thereby gather more pollen. Studies have shown that queen bumblebees transfer up to 4 X as much pollen as honeybees; worker bumblebees transfer approximately twice as much pollen [5]. However, more pollen is not always better; what is needed is enough pollen to result in fertilization of all the pistils. Extra pollen will not have an effect. The amount of pollen required for each flower varies depending on the plant species. A flower that has not been adequately pollinated continues to produce nectar so as to continue to attract pollinators it is usually only when full pollination has occurred that nectar flow stops. Bumblebees are large and strong and in some crops they tear holes in the sides of the flowers which allow access to the nectaries without depositing pollen on the pistils. This has been noted in blueberries and causes further decreases in pollination because other pollinators such as honeybees learn to use these holes made by the bumblebees [6].

Can native insect and bee pollinators be relied on?

Whether native pollinators will be adequate to pollinate a crop will depend on a number of factors:

The size of the crop

The kind of crop

The surrounding forage

The neighboring crops

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Today‚Äôs farming practices are intensive and provide few places for native pollinators to live. Any crop that is surrounded by heavily farmed land will be deficient in native pollinators especially if the surrounding crops provide more attractive forage. Native bees are considered to be particularly undependable pollinators for some plants, such as blueberries, because of the high number of flowers involved and intensive cultivation [2]. To rely on native pollinators one should ensure that the acreage is small and surrounded by grasslands or low lying shrubs.

The major disadvantage with native pollinators is that their numbers in any year cannot be assurance. Many factors such as weather, pesticide spraying and human activity can have a significant affect on the numbers from year to year. It may not be until after the bloom is finished that a grower find out that pollinators were too low in abundance.

Honeybees are effective pollinators and provide the best value

While other bees may transfer more pollen, honeybees are the best choice of pollinator in all but a few specialty crops. Honeybee colonies have populations that are thousands of times greater than any other bee species. As a result there are far more bees to go out and pollinate. Honeybees were one of the first animals to be domesticated. Because of this they are easier to manage and move than any other bee species since management techniques have developed over thousands of years.

Hives should be effectively placed for maximal pollination

Contrary to the information given in many publications it is not necessary to spread beehives throughout the field as scientific studies have shown that pollination effectiveness does not decrease substantially until beehives are more than 2.5 km from the blueberry plants [7]. Pollination will be most efficient if the hives are located in groups near the centre of the field. They should be easily accessible to facilitate management of the hives. Growers should accept that the bees will fly considerable distances while foraging and this will result in nearby fields also being pollinated. As bees will regularly fly 2 km while foraging, inadequate pollination is an indicator of insufficient numbers of pollinators, not poor distribution.

Colonies should be placed in a sunny location, near water and protected from the wind. Wind seriously reduces foraging activity. [8]

Not all beehives are the same. While in general most farmers arrange for pollination of their blueberry crops, many often put some hives near the blueberries but do not consider the quality of the hives. Not all bees are the same, just as not all fertilizer is the same. Care should be taken to ensure that the bees are doing what they are supposed to be doing.

For blueberry pollination expect to pay $65-85 per hive in 2006. The beehives should be sufficiently strong. This means 5+ frames of brood and 8+ frames covered with bees at the start of bloom. Do not use substandard hives for pollination as hives with less than 4 frames of brood will be too small to do any significant pollinating and are not worth any fee that you pay. The stronger a hive is the more effective at pollination it will be. A hive of 20 000 bees is more than 3 times more effective than two hives of 10 000 bees. Therefore, paying $15 more for a hive that is twice as strong is a very cost-effective method of improving yield. If you have any doubts about the strength of your hives you should contact your beekeeper. If talking with your beekeeper does not reassure you about the quality of the hives placed for pollination contact the provincial Apiculturist, Paul van Westendorp, 604 556-3129 This email address is being protected from spambots. You need JavaScript enabled to view it..

Almond growers in California have learnt the value of pollination and around 1.4 million colonies are used in almond pollination every year (about half the total number of hives in the United States). Last year, a shortage of hives caused by large numbers of hives killed by Varroa mites caused a significant increase in the pollination price. Prices rose from $75 US to $110-125 US and some reports mention that growers scrambling for bees as the season started paid $150 US per hive. The almond pollination industry hires independent or former beekeepers to check the strength of the hives and ensure that the hive meets the requirements.

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Advantages of Honeybees

Honeybees are easily managed in artificial hives

Honeybees can be easily moved into and out of fields in bloom and quickly adapt to new surroundings

Honeybees have excellent spatial and memory capabilities and can communicate the location of rich floral sources quickly to other members of the hive allowing bees to quickly mobilize to pollinate flowers that are available for short periods such as large acreages of uniform berry crops.

Honeybees are more adaptable and are capable of manipulating and pollinating complex flowers that cannot be pollinated by other generalist species.

Honeybees will forage further than other bees

Disadvantages of Honeybees

Honeybees are defensive and can sting if provoked

Honeybees tend not to fly below temperatures of 10 ¬?C.

Honeybees will switch quickly to flowers that are yielding better than the crop being pollinated (especially true for cranberries)

How to tell if you are getting adequate pollination

Blueberry flowers lose their corolla soon after pollination, giving the field a ‚Äúgreenish‚Äù appearance once new flowers stop appearing. Other signs of adequate pollination include the ease of separating the corolla from the plant when flowers are brushed by a hand. The appearance of the fruit is also a good indicator as poorly pollinated fruit tend to be misshapen. Measuring yields at harvest is not always indicative of pollination success since other factors such as diseases, pests, and weather have significant effects on yield.

A method for quantitatively measuring pollination success requires marking a loose cluster with a thread or ribbon at or just before bloom starts. At this stage, flowers above the mark can be counted before they open. The blooms can then be assessed every 7-10 days to determine fruit set and bees can be added as necessary. A week after bloom has ended, fruit set should be assessed (the percent of set fruit relative to the initial number of flowers). Later, by the middle of June (2-3 weeks after bloom), after flowers drop, the percent of remaining berries held on the plant that should mature can be estimated by counting the fruit and determining the proportion of fruit relative to the initial number of flowers. At least 30 representative bloom clusters, throughout a field, should be used in these estimates. Any frost damage, and insect or disease damage should be taken into account in determining whether these estimates reflect pollination or whether they might also include other factors.

Honeybees are the most cost-effective way of increasing yield.

The economic benefits of good honeybee hives can be considerable. In general, growers have seen a correlation between yield and the stocking rate of beehives up to 5 hives per acre [8, 9]. This agrees with scientific data from the Lower Mainland which indicates that for optimal berry size, flowers on the cultivar ‚ÄúBluecrop‚Äù require 125 pollen grains to be deposited on each flower [10]. This corresponds to approximately 3-4 visits to each flower from bumblebees and 8-9 visits from honeybees [11].

Scheduling Delivery of Colonies Try to schedule the delivery of honey bee colonies to coincide with 10-25% bloom. Early contact with the beekeeper is helpful for both parties. Keep in contact and inform the beekeeper when bloom will start.

Checklist of things to watch for in beehives

Ensure that you have the correct kind of bees for your crop. Honeybees for large acreages of berry crops, bumblebees for greenhouse crops.

Contact your beekeeper early in the season to ensure that there will be enough bees to meet your requirements. Then keep in contact with your beekeeper as the blooming season gets closer.

Ensure that the bees are delivered by 10-25% bloom.

Ensure that the colonies are strong enough.

Ensure that the beekeeper manages the hives effectively ‚Äì In general this means the hives are checked when they are first placed in the field and then every 2-3 weeks after placement.

Colonies should be placed in a sunny location and protected from the wind.